Method of preparing indium antimonide films



United States Patent() assignments, to International Business Machines Corporation, Endieott, NX., a corporation Filed Apr. 5, 1961, Ser. No. 1041,969 4 Claims. (Cl. 117-201) This invention relates to the method of preparing thin films @and more particulanly to a method tor preparing thin nlm-s of stoiclhiometric indium lantimonide.

'Ilhin lms of semiconductors can be made by several techniques, but the preparation of stoichiometric films of binary compounds, such as indium antimonide, is diicult. It has been found that vacuum evaporation of a compound such as indium antirnonide usually results in a film which does not possess true stoichiometric properties and is, therefore, unsuitable for semiconductor applications; apparently during evaporation, tractionation c-f the components takes place and the deposited film has a composition different from `that .of the original material. Assuming a beam of molecules, some of the molecules acqure velocity components in directions off the axis of the beam because of collisions, and the magnitudes of these components are a function :of molecular weight. In a vapor beam comprising indium antimonide, lfor example, indium atoms are deflected more than indium antimunide 'or antimony molecules. Although the excess of a volatile element can lbe removed from 1a deposited film Iby heating, this is not ia completely satisfactory procedure since the loss of the volatile element leaves many imperfections, even if considerable recrystallization takes place. Therefore, a method is required obtains :deposition of a stoichiometric composition in all stages of film formation.

Accordingly, it is a principal object of the present invention 'an improved method for forming stoichiometric lms of indium rantimonide.

It is ,another object of lthe invention to provide an irnproved method for forming stoichiometric til-ms orf indium antimonide by vapor techniques which films are suitable for use in semiconductor devices.

lIt is yet another `object of the present invention to ptovide an improved method for forming indiumantimonide films wlhich method is usable in commercial production of semiconductor devices.

In one form, the invention provides. ran improved method `of forming a stoichiometric indium antimonidle film comprising the steps of reacting the vapors or indium dimethyl and stibline 'at about room tempenature over la stable substrate to form a film of la coeordination compound, and heating said compound .at 150 C. or higher to eliminate methane and form an indium antimonide The (foregoing and other objects, features land advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 shows a schematic drawing roflan apparatus [tor practicing the method or pnocess according to the invention.

fFIG. 2 shows a block `diagram illustnative of the genenal method of the invention.

FIG. 3 shows a block diagram of the detailed steps of the method `of the invention.

As noted above, indium antimonide films l.have heretofore been formed by vacuum evaporation of the cornpound. However, because of dissociation in the vapor,

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the ,deposited films have poor electrical characteristics, and they usually deviate from stoichiometric composition.

A principal feature of the method according to the invention is that the vapors ccf trimethyliudium or indium trimethyl, In(CH3)3, and stibine, SbH3, are reacted at about room temperature over la stable substrate to provide .la film having a composition suitable for conversion to a useful stoichiometric semiconductor. 'Ilhe general method is indicated in the block diagram of PIG. 2.

Preparatory to utilizing the method lof the invention, trimethylindium isfprepared by the reaction of dimethylmercury with indium, as is in the art; stibine is prepared 'by the lhydfnolysis of magnesium antimony in concentrated [hydrochloric acid and purified by rfractional distillation Iand condensation, as is also known in the art.

Referring to FIG. 1, the system 11 in wlhich the stibine and trimethylindium rare reacted comprises ra `first rtrap lor bight portion 13, a reaction chamber 1'4 in which la sub'- strate 15 to be plated is positioned, and -a second trap or bight portion y17. llhe substrate 15 may be :of glass, quartz, silicon or other material on which a semiconductive film can be deposited.

The system 11 is initially evacuated. Chamber 14 is maintained at room temperature. The first cycle of the process is then initiated.

FIG. 2 sho-ws in block diagram fform the pnocess of the invention. In FIG. 3, the pnocess is arbitrarily divided into cycles and steps to 'facilitate the exp ian'ation.

Stibine is introduced through suitable valve means l16 to the trap 13 in the left-hand end, las oriented in FIG. V1 of reaction system 11. Trimet-hylindium is introduced through suitable valve means 18 to the trap 17 in the right-hand end of the system 11. 'llhe trap` 13 is surrounded by a bath 19 of liquid nitrogen to decrease the temperature of the stibiue to C.; the pressure of the stibine will become negligible. The ltrap 17' is surrounded by a bath 2.1 also of liquid nitrogen to also decnease the 'tempenature of trimethylindium to 195 C.; the pressure of the trimethylindium will falso be negligible At this point, stibine is conde-used in trap 13 and trimethylindiurn is condensed in tnap y17 while the system is evacuated (step #1). l

Next (step #2), bath 19 is removed from trap 13 and a second bath similar to bath `19 but containing, say canb'on disulfide, is substituted therefor. The carbon disulfide bath causes the temperature of the triap l13 to rise to -112 C.; the pressure of stibifne will increase to about 2 mm. 'Ilhe stibine will tend to move to-wlard chamber 14. At the same time, hath 21 is removed dimm trap 17 and the temperature of the trimethylindium increases to room tempenature; the pressure of the .trimethylindiurn will incnease to about 2 mm. Tlhe trimethyliudium will move trom the Warmer `area of tnap 17 through the .chamber 14 toward trap 13; this step is continued until all the trimethylindiurn is depleted from trap 17 fwhich can be indicated by suitable manometers.

The stibine and tnimethylindium will react in chamber 14 to produce a co-ordination compound or, more specifically, a non-volatile orange film on substrate 15. Essentially, the foregoing comprises a complete process; however, to obtain films of thicker dimensions the cycling operation is continued.

As noted, during the foregoing steps, the trimethylindium will be moved out of trap 17 and will condense in the trap 13. Both trimethylindium `and stibine Will now be in trap 13; stibine will have a pressure of about 2 mm.; the pressure of the trimethylindium will be negligible and the trimethylindium will condense.

At this point in the process, trap 13 is at l|12 C. and trap 17 is yat room temperature. The second bath of carbon disulfide is now removed from trap 13 and a third bath, which may be composed of Dry Ice, is provided for trap 13 (step #3). Dry Ice changes the temperature of trap 13 to \78.5 C.; the pressure of stibine will be about 34 mm. At the same time that the Dry Ice bath is placed around trap 113, a bath of carbon disulfide is placed around trap 17 to decrease ihe temperature of trap 1'7 to 112 C. As noted, at -112 C., the pressure of stibine is 2 mm.; since stibine pressure in trap 13 is relatively high (34 mm.) with respect to trap 17 (2 mm), all the stibine Will move relatively fast out of trap A113 toward trap 17.

After the stibine is transferred out of trap 13, as can be indicated by suitable manometers, the carbon disulfide bath around trap 13` is removed and trap 113 is permitted to Warm to room temperature (step #4). The trimethylindium will move from [the Warmer area of trap 13 through the reaction chamber 14 to the trap 17 which is at i- 112 C. The trimethylindium will react with stibine in the chamber 14 to cause a second coating of a film to be formed on substrate 15.

k The second cycle is then initiated by placing a Dry Ice bath at 781 C. on trap 17 to cause all the stibine to transfer out of trap 17; at this point, trap 113` is at a 112 C. Next, the bath at 78 C. is removed from trap 17 and the temperature of trap 17 is permitted to increase to room temperature; the pressure of the trimethylindium is 2 mm. The trimethylindium will move from the Warmer area of trap 17 through chamber 14 toward trap 131. The trimethylindium Will react with the stibine in chamber 14- to yform another layer of film on substrate 1S.

As shown in FIG. 3, the third cycle repeats steps #3 and #4 of the first cycle, and the fourth cycle repeats the two steps of the second cycle. The fifth cycle repeats the third cycle; the sixth cycle repeats the steps of the fourth cycle, etc. As many cycles as necessary to provide a film of the desired thickness are made.

After a film of desired thickness is obtained, the substrate is heated to 150 C. or hotter. The lm formed on the substrate decomposes at about 150 C. to a shiny black film which is essentially indium antimonide (InSb).

The chemical reaction is believed to be:

Room temperature InMes-l- SbHa MeiInSbHz-l- CHi Heat to 150 C.

InSb+2CH4 (Note: Me=CH3 Control of the partial pressure of stibine is important since, at higher pressures, antimony metal may be formed; it has been found that When a stibine pressure of 2 mm. is maintained, a stoichiometric film is formed.

If the deposition of the film is attempted at temperatures above normal room temperature, excess free antimony deposits and the film produced by the heating at ;150 C. or higher does not provide stoichiometric indium antimonide. The presence of excess iantimony is inferred from the fact that stiibine alone deposits antimony at temperatures 'above 35 C., and the deviation from stoichiometry in the films is indicated by small variation in resistance with temperature changes which are dharacteristie of metallic conduction. Stoichiometric films formed in accordance with the invention increase in resistance by a factor of about 100 when cooled from 300 K. to 77 K.

While the invention has been particularly shown and described With reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes lin vform and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. The method of forming semiconductive films on a substrate placed in an evacuated chamber comprising the steps of, reacting vapors of ltrimethylindium and stibine over said substrate at room temperature and at a pressure of about 2 mm. to form a coating on said substrate and 5 heating said substrate to a temperature in the range of 150 C. for decomposing said coating to form an indium antimonide film on said substrate.

2. A method of forming semiconductive films on a substrate utilizing a system including a reaction chamber and first and second traps comprising, the steps of, evacuating said system, placing a substrate to be coated in said reaction chamber, maintaining said chamber at room temperature, introducing stibine into said first trap, cooling and thereby condensing said stibine in said first trap, introducing trimethylindium linto said second tray, cooling and thereby condensing trimethylindium in said second trap, raising the temperature of said stibine to vaporize said stibine and to increase the vapor pressure of said stibine to about 2 mm., channeling said vaporized stibine from said rst trap into said chamber, raising the temperature of said trimethylindium to vaporize said trimethylindium and to increase the vapor pressure of said trimethylindium to about 2 mm., channel-ing said vaporized trimethylindium from said second trap into said chamber, whereby said stibine and said trimethylindium react in sm'd chamber to form a coating on said substrate, and heating said substrate to a 'temperature in the range of C. for thermal-ly decomposing said coating to form stoichiometric films of indium antimonide on said substrate.

3. A. method of forming semiconductive films on a substrate utilizing a system including a reaction chamber intermediate a first and a second trap comprising the steps of evacuating said system, maintaining said reaction chamber at room temperature, introducing stibine into said rst trap, cooling and lthereby condensing stibine in said first trap, introducing trimethylindium into said second trap, cooling and thereby condensing trimethylindium in said second trap, raising the temperature of said first trap to increase the stibine vapor pressure to about 2 mm. whereby stibine tends to pass into said reaction chamber, raising the temperature of said second trap to increase the trimethylindium vapor pressure to about 2 mm. whereby the trimethylindium moves from the higher temperature area of said second trap through the reaction chamber to said first trap to cause the stibine and trimethylindium to react in said chamber to form a coating on said substrate, raising the temperature of said first trap to increase the vapor pressure of the stibine to about 34 mm. to cause said stibine to move out of said rst trap toward said second trap whereby the trimethylindium will be in said first trap and the stibine will be in said second trap, raising the temperature of said first trap to increase the Vapor pressure of trimethylindium to about 2 mm. wherein said trimethylindium will begin to transfer back through said reaction chamber to said second trap and stibine will move into said reaction chamber whereby the stibine and trimethylindium. will react to provide a second coating on said substrate.

4. A method according to claim 3 and including the step of heating the film formed on said substrate to approXimately ,150 C. to form an indium antimonide film.

References Cited in the tile of thispatent UNITED STATES PATENTS 869,013 McQua-t Oct. 22, 1907 2,701,216 Seiler Feb. 1, 1955 2,778,743 Bowman Ian. 22, 1957 2,938,816 Gunther May 3l, 1960 

1. THE METHOD OF FORMING SEMICONDUCTIVE FILMS ON A SUBSTRATE PLACED IN AN EVACUATED CHAMBER COMPRISING THE STEPS OF, REACTING VAPORS OF TRIMETHYLINDIUM AND STIBINE OVER SAID SUBSTRATE AT ROOM TEMPERATURE AND AT A PRESSURE OF ABOUT 2 MM. TO FORM A COATING ON SAID SUBSTRATE AND HEATING SAID SUBSTRATE TO A TEMPERATURE IN THE RANGE OF 150* C. FOR DECOMPOSING SAID COATING TO FORM AN INDIUM ANTIMONIDE FILM ON SAID SUBSTRATE. 